This invention relates to a material for low-maintenance sliding surface bearings, which material comprises a metallic backing and a bearing layer having a thickness of 30 to 500 .mu.m and consisting of a mixture of polyvinylidene fluoride(PVDF) and at least one additive for improving the friction and sliding properties.
European Patent Specification No. 44 577 discloses for use in low-maintenance sliding surface bearings a material consisting of a steel backing, a bronze layer and a bearing layer. A porous layer having a thickness of 250 to 350 .mu.m has been sinter-bonded to the steel backing. The bearing layer has a thickness of 30 to 500 .mu.m and consists of a mixture of 30 to 60% by weight PVDF and 20 to 50% by weight lead. The open pores of the bronze layer are also completely filled with said mixture. The mixture of PVDF and lead may optionally contain 5 to 30% by weight polytetrafluorethylene (PTFE). That material for sliding surface bearings exhibit in operation that mechanical-technological and physical behavior which is usually expected from similar materials for sliding surface bearings comprising a backing and a bearing layer, which is bonded to the backing and comprises a matrix consisting of fluorine-containing polymeric material and lead powder as an additive, but has the advantage that it can be machined when the bearing has been installed so that lubricating pockets and/or lubricating grooves can be formed in the bearing surface. Because the bearing layer can be machined when the bearing has been installed, it is possible to subject installed bushings to reaming or precision-turning, e.g., in order to compensate misalignments or to provide smaller bearing clearances.
In a grease-lubricated sliding surface bearing, such a material will suffer only an extremely small wear while the bearing is run in and, e.g., under a load of below 10 N/mm.sup.2 and a high sliding velocity of up to 3 meters per second said wear amounts to about 0.0015 mm. Because the sliding surface bearings made of such a material require a relubrication only after relatively long intervals of time, they constitute low-maintenance bearings. But owing to the lead powder contained in the matrix of the bearing layer that material for sliding surface bearings cannot be used in certain technical fields in which hygiene is significant, for instance, in household appliances, packaging machines and medical-equipment and in machines for processing foodstuffs and for producing pharmaceutic materials.